Cardiac pacemakers stimulate the heart beat by means of electrical impulses which are introduced into the muscle tissue of the heart. For this purpose, a cardiac pacemaker is usually implanted, for example, near the shoulder of the thoracic cage, at least one probe or electrical lead being guided from the implanted cardiac pacemaker via a vein into the atrium or the chambers of the heart and anchored there. The electrical lead is problematical or disadvantageous. This runs over a length of about 30 cm in the blood circulation system and can thereby cause undesirable or even fatal physical reactions. Furthermore, the risk of failure of the probes or leads due to material fatigue as a result of the severe mechanical stressing during body movements is particularly high. Another complication frequently encountered is dislocation of the probes triggered by movements of the patient.
Stimulation by magnetic impulses has been proposed, for example, in U.S. Pat. No. 5,170,784 A in order to avoid the electrical lead and the electrode. However, purely magnetic stimulation does not function satisfactorily so that magnetically stimulating cardiac pacemakers have not been generally accepted.
U.S. Pat. No. 5,411,535 A discloses a cardiac pacemaker with an implantable control device and a separate electrode device. Electrical signals of 10 MHz to a few GHz in particular are transmitted without wires between the control device and the electrode device for controlling the electrode device. The actual power supply of the electrode device is provided via a battery integrated in the electrode device. Such cardiac pacemakers with a separate electrode device have not been widely accepted so far. This may be because the electrode device is of a considerable size and has a limited operating time because of the battery.
The article “A Surgical Approach to the Management of Heart-Block Using an Inductive Coupled Artificial Cardiac Pacemaker” by L. D. Abrams et. al., published in the journal “The Lancet”, 25 Jun. 1960, pages 1372 to 1374, describes a method for stimulating a heart where an external control device comprising a coil to be located externally on the body is inductively coupled to a coil implanted between the skin and the ribs. Two electrical leads led from the implanted coil to two electrodes in the heart muscle. Apart from the fact that an external control device is generally problematical and not desirable, the wiring between the implanted coil and the electrodes at a distance therefrom results in the same problems as in the usual cardiac pacemaker described above where at least one electrode is connected to the implanted cardiac pacemaker via an electrical lead through a vein. Furthermore, the implantation of a pacemaker system requires opening the thoracic cage and involves an open-heart operation. Moreover, the implanted coil is very sensitive to external electromagnetic fields so that undesirable interfering voltages are induced and appear at the electrodes.
JP 06 079 005 A discloses an implantable cardiac pacemaker whose battery can be inductively recharged from outside via a coil.
U.S. Pat. No. 5,405,367 A discloses an implantable microstimulator. The microstimulator comprises a receiving coil, an integrated circuit and electrodes. It can be supplied with energy and with control information via an external magnetic field generated by an external coil having an allocated oscillator and an allocated stimulation control device. Such a microstimulator is not suitable for cardiac stimulator or as a cardiac pacemaker since it is relatively large for sufficient capacity and requires an external energy supply.
WO 2006/045075 A1 relates to various configurations of systems that employ leadless electrodes to provide pacing therapy. In particular, a single magnetic pulse is used to generate an electrical pulse in an electrode device. This is problematic, in particular due to magnetic saturation.